U.S. patent application number 12/625853 was filed with the patent office on 2010-06-10 for method and apparatus for controlling a wind turbine.
Invention is credited to Andreas Kirchner, Hartmut Scholte-Wassink, Enno Ubben.
Application Number | 20100140939 12/625853 |
Document ID | / |
Family ID | 42230232 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100140939 |
Kind Code |
A1 |
Scholte-Wassink; Hartmut ;
et al. |
June 10, 2010 |
METHOD AND APPARATUS FOR CONTROLLING A WIND TURBINE
Abstract
A power system for a wind turbine having a measurement device
configured to detect an overfrequency condition within an
electrical system and a controller communicatively coupled to the
measurement device. The controller is configured to switch the wind
turbine between a power generation mode and a power consumption
mode based on an existence of a detected overfrequency
condition.
Inventors: |
Scholte-Wassink; Hartmut;
(Lage, DE) ; Kirchner; Andreas; (Osnabrueck,
DE) ; Ubben; Enno; (Steinfurt, DE) |
Correspondence
Address: |
PATRICK W. RASCHE (22402);ARMSTRONG TEASDALE LLP
ONE METROPOLITAN SQUARE, SUITE 2600
ST. LOUIS
MO
63102-2740
US
|
Family ID: |
42230232 |
Appl. No.: |
12/625853 |
Filed: |
November 25, 2009 |
Current U.S.
Class: |
290/44 |
Current CPC
Class: |
F03D 7/0272 20130101;
F05B 2260/903 20130101; F03D 7/042 20130101; F03D 9/255 20170201;
F05B 2270/337 20130101; Y02E 10/723 20130101; Y02E 10/72 20130101;
F03D 7/0224 20130101; Y02E 10/725 20130101; F03D 7/0284
20130101 |
Class at
Publication: |
290/44 |
International
Class: |
F03D 7/00 20060101
F03D007/00; F03D 9/00 20060101 F03D009/00 |
Claims
1. A power system for a wind turbine, said power system comprising:
a measurement device configured to detect an overfrequency
condition within an electrical system; and, a controller
communicatively coupled to said measurement device, said controller
configured to switch the wind turbine between a power generation
mode and a power consumption mode based on an existence of a
detected overfrequency condition.
2. A power system in accordance with claim 1, wherein said
controller is further configured to switch the wind turbine from
the power generation mode to the power consumption mode when the
overfrequency condition is detected.
3. A power system in accordance with claim 1, wherein said
controller is further configured to: generate at least one of a
negative torque command and a negative power command when the
overfrequency condition is detected; and, generate at least one of
a positive torque command and a positive power command when the
overfrequency condition is not detected.
4. A power system in accordance with claim 1, further comprising at
least one blade, said controller being further configured to pitch
said blade to a predefined position when the overfrequency
condition is detected.
5. A power system in accordance with claim 4, further comprising a
generator communicatively coupled to said controller, said
generator configured to use power from the electrical system to
rotate said blade when the overfrequency condition is detected.
6. A power system in accordance with claim 5, further comprising a
four quadrant power converter coupled to said generator, said four
quadrant power converter configured to rotate said generator and to
brake said generator in both a clockwise direction and a
counterclockwise direction, respectively.
7. A power system in accordance with claim 1, wherein said
measurement device comprises a current transformer coupled to the
electrical system.
8. A wind turbine operatively coupled to an electrical system, said
wind turbine comprising: a generator configured to be coupled to
the electrical system; a measurement device operatively coupled to
the electrical system and configured to detect an overfrequency
condition within the electrical system; and, a controller
communicatively coupled to said measurement device, said controller
configured to switch said wind turbine between a power generation
mode and a power consumption mode based on an existence of a
detected overfrequency condition.
9. A wind turbine in accordance with claim 8, wherein said
controller is further configured to switch said wind turbine from
the power generation mode to the power consumption mode when the
overfrequency condition is detected.
10. A wind turbine in accordance with claim 8, wherein said
controller is further configured to: generate at least one of a
negative torque command and a negative power command when the
overfrequency condition is detected; and, generate at least one of
a positive torque command and a positive power command when the
overfrequency condition is not detected.
11. A wind turbine in accordance with claim 8, further comprising
at least one blade, said controller being further configured to
pitch said blade to a predefined position when the overfrequency
condition is detected.
12. A wind turbine in accordance with claim 11, wherein said
generator is configured to use power from the electrical system to
rotate said blade when the overfrequency condition is detected.
13. A wind turbine in accordance with claim 8, further comprising a
four quadrant power converter coupled to said generator, said four
quadrant power converter configured to rotate said generator and to
brake said generator in both a clockwise direction and a
counterclockwise direction, respectively.
14. A wind turbine in accordance with claim 8, wherein said
measurement device comprises a current transformer coupled to the
electric system.
15. A method for controlling a wind turbine, said method
comprising: coupling a generator to the wind turbine and to an
electrical system; detecting an overfrequency condition within the
electrical system; and, switching the generator between a power
generation mode and a power consumption mode based on an existence
of a detected overfrequency condition.
16. A method in accordance with claim 15, further comprising
configuring a controller to switch the wind turbine from the power
generation mode to the power consumption mode when the
overfrequency condition is detected.
17. A method in accordance with claim 16, further comprising
configuring the controller to: generate at least one of a negative
torque command and a negative power command when the overfrequency
condition is detected; and, generate at least one of a positive
torque command and a positive power command when the overfrequency
condition is not detected.
18. A method in accordance with claim 15, wherein the wind turbine
includes at least one blade rotatably coupled to the wind turbine,
said method further comprising pitching the blade to a predefined
position when the overfrequency condition is detected.
19. A method in accordance with claim 18, further comprising
configuring the generator to use power from the electrical system
to rotate the blade when the overfrequency condition is
detected.
20. A method in accordance with claim 15, further comprising:
coupling a four quadrant power converter to the generator; and,
configuring the four quadrant power converter to rotate the
generator and to brake the generator in both a clockwise direction
and a counterclockwise direction, respectively.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter described herein relates generally to
wind turbines and, more particularly, to a method and apparatus for
controlling a wind turbine.
[0002] Generally, a wind turbine includes a rotor that includes a
rotatable hub assembly having multiple blades. The blades transform
wind energy into a mechanical rotational torque that drives one or
more generators via the rotor. The generators are sometimes, but
not always, rotationally coupled to the rotor through a gearbox.
The gearbox steps up the inherently low rotational speed of the
rotor for the generator to efficiently convert the rotational
mechanical energy to electrical energy, which is fed into a utility
grid via at least one electrical connection. Gearless direct drive
wind turbines also exist. The rotor, generator, gearbox and other
components are typically mounted within a housing, or nacelle, that
is positioned on a base that includes a truss or tubular tower.
[0003] Some wind turbine configurations include double-fed
induction generators (DFIGs). Such configurations may also include
power converters that are used to convert a frequency of generated
electric power to a frequency substantially similar to a utility
grid frequency. Moreover, such converters, in conjunction with the
DFIG, also transmit electric power between the utility grid and the
generator. A wound rotor of the DFIG also receives excitation power
from one of the connections to the utility grid.
[0004] Electric utility grids are often designed to operate at
specified frequencies, or within specified frequency ranges.
Certain events, such as an overproduction of power, may increase
the utility grid frequency above a predefined frequency limit (also
known as overfrequency conditions). If not corrected, such
overfrequency conditions may cause damage to utility grid
components and/or to loads that are coupled to the utility grid. At
least some known power systems reduce a power output of one or more
generators in response to overfrequency conditions. However, such
reduction of power may be slow, and existing overproduction of
power may persist while the generator reduces its power output.
BRIEF DESCRIPTION OF THE INVENTION
[0005] In one embodiment, a power system for a wind turbine is
provided that includes a measurement device configured to detect an
overfrequency condition within an electrical system and a
controller communicatively coupled to the measurement device. The
controller is configured to switch the wind turbine between a power
generation mode and a power consumption mode based on an existence
of a detected overfrequency condition.
[0006] In another embodiment, a wind turbine operatively coupled to
an electrical system is provided that includes a generator
configured to be coupled to the electrical system, a measurement
device operatively coupled to the electrical system and configured
to detect an overfrequency condition within the electrical system,
and a controller communicatively coupled to the measurement device.
The controller is configured to switch the wind turbine between a
power generation mode and a power consumption mode based on an
existence of a detected overfrequency condition.
[0007] In yet another embodiment, a method for controlling a wind
turbine is provided that includes coupling a generator to the wind
turbine and to an electrical system. An overfrequency condition is
detected within the electrical system and the generator is switched
between a power generation mode and a power consumption mode based
on an existence of a detected overfrequency condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective view of a portion of an exemplary
wind turbine.
[0009] FIG. 2 is a schematic view of an exemplary electrical and
control system suitable for use with the wind turbine shown in FIG.
1.
[0010] FIG. 3 is a block diagram of an exemplary power system
suitable for use with the electrical and control system shown in
FIG. 2.
[0011] FIG. 4 is a flowchart of an exemplary method for controlling
a wind turbine suitable for use with the power system shown in FIG.
3.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The embodiments described herein use a measurement device to
detect an overfrequency condition within an electrical system, such
as an electrical utility grid. If an overfrequency condition is
detected, a controller transmits one or more pitch commands to a
pitch system that rotates one or more blades of a wind turbine to a
predefined controlled position. The controller switches a generator
from a power generation mode to a power consumption mode. The
controller transmits one or more negative torque commands and/or
one or more negative power commands to a power converter. The power
converter generates a rotor current based on the torque commands
and/or the power commands. The power converter transmits the rotor
current to a generator rotor. Power from the electrical utility
grid is also transmitted to and consumed by the generator. The
rotor current induces a torque to a rotor shaft that is coupled to
the wind turbine blades and the rotor shaft rotates the wind
turbine blades. Power is consumed from the electrical utility grid
in order to reduce or minimize the overfrequency condition.
[0013] FIG. 1 is a perspective view of a portion of an exemplary
wind turbine 100. Wind turbine 100 includes a nacelle 102 housing a
generator (not shown in FIG. 1). Nacelle 102 is mounted on a tower
104 (a portion of tower 104 being shown in FIG. 1). Tower 104 may
have any suitable height that facilitates operation of wind turbine
100 as described herein. Wind turbine 100 also includes a rotor 106
that includes three blades 108 attached to a rotating hub 110.
Alternatively, wind turbine 100 includes any number of blades 108
that facilitates operation of wind turbine 100 as described herein.
Blades 108 are spaced about hub 110 to facilitate rotating rotor
106, thereby transferring kinetic energy from wind 111 into usable
mechanical energy, and subsequently, electrical energy. In the
exemplary embodiment, wind turbine 100 includes a gearbox (not
shown in FIG. 1) operatively coupled to rotor 106 and a generator
(not shown in FIG. 1).
[0014] FIG. 2 is a schematic view of an exemplary electrical and
control system 200 that may be used with wind turbine 100. Rotor
106 includes blades 108 coupled to hub 110. Rotor 106 also includes
a low-speed shaft 112 rotatably coupled to hub 110. Low-speed shaft
112 is coupled to a step-up gearbox 114 that is configured to step
up the rotational speed of low-speed shaft 112 and transfer that
speed to a high-speed shaft 116. In the exemplary embodiment,
gearbox 114 has a step-up ratio of approximately 70:1. For example,
low-speed shaft 112 rotating at approximately 20 revolutions per
minute (rpm) coupled to gearbox 114 with an approximately 70:1
step-up ratio generates a speed for high-speed shaft 116 of
approximately 1400 rpm. Alternatively, gearbox 114 has any suitable
step-up ratio that facilitates operation of wind turbine 100 as
described herein. As a further alternative, wind turbine 100
includes a direct-drive generator that is rotatably coupled to
rotor 106 without any intervening gearbox.
[0015] High-speed shaft 116 is rotatably coupled to generator 118.
In the exemplary embodiment, generator 118 is a wound rotor,
three-phase, double-fed induction (asynchronous) generator (DFIG)
that includes a generator stator 120 magnetically coupled to a
generator rotor 122. In an alternative embodiment, generator rotor
122 includes a plurality of permanent magnets in place of rotor
windings.
[0016] Electrical and control system 200 includes a turbine
controller 202. Turbine controller 202 includes at least one
processor and a memory, at least one processor input channel, at
least one processor output channel, and may include at least one
computer (none shown in FIG. 2). As used herein, the term computer
is not limited to integrated circuits referred to in the art as a
computer, but broadly refers to a processor, a microcontroller, a
microcomputer, a programmable logic controller (PLC), an
application specific integrated circuit, and other programmable
circuits (none shown in FIG. 2), and these terms are used
interchangeably herein. In the exemplary embodiment, memory may
include, but is not limited to, a computer-readable medium, such as
a random access memory (RAM) (none shown in FIG. 2). Alternatively,
one or more storage devices, such as a floppy disk, a compact disc
read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a
digital versatile disc (DVD) (none shown in FIG. 2) may also be
used. Also, in the exemplary embodiment, additional input channels
(not shown in FIG. 2) include, without limitation, computer
peripherals associated with an operator interface such as a mouse
and a keyboard (neither shown in FIG. 2). Further, in the exemplary
embodiment, additional output channels may include, without
limitation, an operator interface monitor (not shown in FIG.
2).
[0017] Processors for turbine controller 202 process information
transmitted from a plurality of electrical and electronic devices
that may include, but are not limited to, voltage and current
transducers. RAM and/or storage devices store and transfer
information and instructions to be executed by the processor. RAM
and/or storage devices can also be used to store and provide
temporary variables, static (i.e., non-changing) information and
instructions, or other intermediate information to the processors
during execution of instructions by the processors. Instructions
that are executed include, but are not limited to, resident
conversion and/or comparator algorithms. The execution of sequences
of instructions is not limited to any specific combination of
hardware circuitry and software instructions.
[0018] Generator stator 120 is electrically coupled to a stator
synchronizing switch 206 via a stator bus 208. In an exemplary
embodiment, to facilitate the DFIG configuration, generator rotor
122 is electrically coupled to a bi-directional power conversion
assembly 210 via a rotor bus 212. Alternatively, generator rotor
122 is electrically coupled to rotor bus 212 via any other device
that facilitates operation of electrical and control system 200 as
described herein. As a further alternative, electrical and control
system 200 is configured as a full power conversion system (not
shown) that includes a full power conversion assembly (not shown in
FIG. 2) similar in design and operation to power conversion
assembly 210 and electrically coupled to generator stator 120. The
full power conversion assembly facilitates channeling electric
power between generator stator 120 and an electric power
transmission and distribution grid 213. In the exemplary
embodiment, stator bus 208 transmits three-phase power from
generator stator 120 to stator synchronizing switch 206. Rotor bus
212 transmits three-phase power from generator rotor 122 to power
conversion assembly 210. In the exemplary embodiment, stator
synchronizing switch 206 is electrically coupled to a main
transformer circuit breaker 214 via a system bus 216. In an
alternative embodiment, one or more fuses (not shown) are used
instead of main transformer circuit breaker 214. In another
embodiment, neither fuses nor main transformer circuit breaker 214
is used.
[0019] Power conversion assembly 210 includes a rotor filter 218
that is electrically coupled to generator rotor 122 via rotor bus
212. A rotor filter bus 219 electrically couples rotor filter 218
to a rotor-side power converter 220, and rotor-side power converter
220 is electrically coupled to a line-side power converter 222.
Rotor-side power converter 220 and line-side power converter 222
are power converter bridges including power semiconductors (not
shown). In the exemplary embodiment, rotor-side power converter 220
and line-side power converter 222 are configured in a three-phase,
pulse width modulation (PWM) configuration including insulated gate
bipolar transistor (IGBT) switching devices (not shown in FIG. 2)
that operate as known in the art. Alternatively, rotor-side power
converter 220 and line-side power converter 222 have any
configuration using any switching devices that facilitate operation
of electrical and control system 200 as described herein. Power
conversion assembly 210 is coupled in electronic data communication
with turbine controller 202 to control the operation of rotor-side
power converter 220 and line-side power converter 222.
[0020] In the exemplary embodiment, a line-side power converter bus
223 electrically couples line-side power converter 222 to a line
filter 224. Also, a line bus 225 electrically couples line filter
224 to a line contactor 226. Moreover, line contactor 226 is
electrically coupled to a conversion circuit breaker 228 via a
conversion circuit breaker bus 230. In addition, conversion circuit
breaker 228 is electrically coupled to main transformer circuit
breaker 214 via system bus 216 and a connection bus 232.
Alternatively, line filter 224 is electrically coupled to system
bus 216 directly via connection bus 232 and includes any suitable
protection scheme (not shown) configured to account for removal of
line contactor 226 and conversion circuit breaker 228 from
electrical and control system 200. Main transformer circuit breaker
214 is electrically coupled to an electric power main transformer
234 via a generator-side bus 236. Main transformer 234 is
electrically coupled to a grid circuit breaker 238 via a
breaker-side bus 240. Grid circuit breaker 238 is connected to
electric power transmission and distribution grid 213 via a grid
bus 242. In an alternative embodiment, main transformer 234 is
electrically coupled to one or more fuses (not shown), rather than
to grid circuit breaker 238, via breaker-side bus 240. In another
embodiment, neither fuses nor grid circuit breaker 238 is used, but
rather main transformer 234 is coupled to electric power
transmission and distribution grid 213 via breaker-side bus 240 and
grid bus 242.
[0021] In the exemplary embodiment, rotor-side power converter 220
is coupled in electrical communication with line-side power
converter 222 via a single direct current (DC) link 244.
Alternatively, rotor-side power converter 220 and line-side power
converter 222 are electrically coupled via individual and separate
DC links (not shown in FIG. 2). DC link 244 includes a positive
rail 246, a negative rail 248, and at least one capacitor 250
coupled between positive rail 246 and negative rail 248.
Alternatively, capacitor 250 includes one or more capacitors
configured in series or in parallel between positive rail 246 and
negative rail 248.
[0022] Turbine controller 202 is configured to receive one or more
voltage and electric current measurement signals from a first set
of voltage and electric current sensors 252. Moreover, turbine
controller 202 is configured to monitor and control at least some
of the operational variables associated with wind turbine 100. In
the exemplary embodiment, each of three voltage and electric
current sensors 252 are electrically coupled to each one of the
three phases of grid bus 242. Alternatively, voltage and electric
current sensors 252 are electrically coupled to system bus 216. As
a further alternative, voltage and electric current sensors 252 are
electrically coupled to any portion of electrical and control
system 200 that facilitates operation of electrical and control
system 200 as described herein. As a still further alternative,
turbine controller 202 is configured to receive any number of
voltage and electric current measurement signals from any number of
voltage and electric current sensors 252 including, but not limited
to, one voltage and electric current measurement signal from one
transducer.
[0023] As shown in FIG. 2, electrical and control system 200 also
includes a converter controller 262 that is configured to receive
one or more voltage and electric current measurement signals. For
example, in one embodiment, converter controller 262 receives
voltage and electric current measurement signals from a second set
of voltage and electric current sensors 254 coupled in electronic
data communication with stator bus 208. Converter controller 262
receives a third set of voltage and electric current measurement
signals from a third set of voltage and electric current sensors
256 coupled in electronic data communication with rotor bus 212.
Converter controller 262 also receives a fourth set of voltage and
electric current measurement signals from a fourth set of voltage
and electric current sensors 264 coupled in electronic data
communication with conversion circuit breaker bus 230. Second set
of voltage and electric current sensors 254 is substantially
similar to first set of voltage and electric current sensors 252,
and fourth set of voltage and electric current sensors 264 is
substantially similar to third set of voltage and electric current
sensors 256. Converter controller 262 is substantially similar to
turbine controller 202 and is coupled in electronic data
communication with turbine controller 202. Moreover, in the
exemplary embodiment, converter controller 262 is physically
integrated within power conversion assembly 210. Alternatively,
converter controller 262 has any configuration that facilitates
operation of electrical and control system 200 as described
herein.
[0024] In the exemplary embodiment, electric power transmission and
distribution grid 213 includes one or more transmission lines 270
(only one shown for clarity) that are coupled to grid bus 242 via a
grid coupling 272. Electric power transmission and distribution
grid 213 is operatively coupled to one or more loads 274 for
providing power to loads 274.
[0025] During operation, wind 111 (shown in FIG. 1) impacts blades
108 and blades 108 transform wind energy into a mechanical
rotational torque that rotatably drives low-speed shaft 112 via hub
110. Low-speed shaft 112 drives gearbox 114 that subsequently steps
up the low rotational speed of low-speed shaft 112 to drive
high-speed shaft 116 at an increased rotational speed. High speed
shaft 116 rotatably drives generator rotor 122. A rotating magnetic
field is induced by generator rotor 122 and a voltage is induced
within generator stator 120 that is magnetically coupled to
generator rotor 122. Generator 118 converts the rotational
mechanical energy to a sinusoidal, three-phase alternating current
(AC) electrical energy signal in generator stator 120. The
associated electrical power is transmitted to main transformer 234
via stator bus 208, stator synchronizing switch 206, system bus
216, main transformer circuit breaker 214 and generator-side bus
236. Main transformer 234 steps up the voltage amplitude of the
electrical power and the transformed electrical power is further
transmitted to electric power transmission and distribution grid
213 via breaker-side bus 240, grid circuit breaker 238 and grid bus
242.
[0026] In the exemplary embodiment, a second electrical power
transmission path is provided. Electrical, three-phase, sinusoidal,
AC power is generated within generator rotor 122 and is transmitted
to power conversion assembly 210 via rotor bus 212. Within power
conversion assembly 210, the electrical power is transmitted to
rotor filter 218 and the electrical power is modified for the rate
of change of the output voltage associated with rotor-side power
converter 220. Rotor-side power converter 220 acts as a rectifier
and rectifies the sinusoidal, three-phase AC power to DC power. The
DC power is transmitted into DC link 244. Capacitor 250 facilitates
mitigating DC link 244 voltage amplitude variations by facilitating
mitigation of a DC ripple associated with AC rectification.
[0027] The DC power is subsequently transmitted from DC link 244 to
line-side power converter 222 and line-side power converter 222
acts as an inverter configured to convert the DC electrical power
from DC link 244 to three-phase, sinusoidal AC electrical power
with pre-determined voltages, currents, and frequencies. This
conversion is monitored and controlled via converter controller
262. The converted AC power is transmitted from line-side power
converter 222 to system bus 216 via line-side power converter bus
223 and line bus 225, line contactor 226, conversion circuit
breaker bus 230, conversion circuit breaker 228, and connection bus
232. Line filter 224 compensates or adjusts for harmonic currents
in the electric power transmitted from line-side power converter
222. Stator synchronizing switch 206 is configured to close to
facilitate connecting the three-phase power from generator stator
120 with the three-phase power from power conversion assembly
210.
[0028] Conversion circuit breaker 228, main transformer circuit
breaker 214, and grid circuit breaker 238 are configured to
disconnect corresponding buses, for example, when excessive current
flow may damage the components of electrical and control system
200. Additional protection components are also provided including
line contactor 226, which may be controlled to form a disconnect by
opening a switch (not shown in FIG. 2) corresponding to each line
of line bus 225.
[0029] Power conversion assembly 210 compensates or adjusts the
frequency of the three-phase power from generator rotor 122 for
changes, for example, in the wind speed at hub 110 and blades 108.
Therefore, in this manner, mechanical and electrical rotor
frequencies are decoupled from stator frequency.
[0030] Under some conditions, the bi-directional characteristics of
power conversion assembly 210, and specifically, the bi-directional
characteristics of rotor-side power converter 220 and line-side
power converter 222, facilitate feeding back at least some of the
generated electrical power into generator rotor 122. More
specifically, electrical power is transmitted from system bus 216
to connection bus 232 and subsequently through conversion circuit
breaker 228 and conversion circuit breaker bus 230 into power
conversion assembly 210. Within power conversion assembly 210, the
electrical power is transmitted through line contactor 226, line
bus 225, and line-side power converter bus 223 into line-side power
converter 222. Line-side power converter 222 acts as a rectifier
and rectifies the sinusoidal, three-phase AC power to DC power. The
DC power is transmitted into DC link 244. Capacitor 250 facilitates
mitigating DC link 244 voltage amplitude variations by facilitating
mitigation of a DC ripple sometimes associated with three-phase AC
rectification.
[0031] The DC power is subsequently transmitted from DC link 244 to
rotor-side power converter 220 and rotor-side power converter 220
acts as an inverter configured to convert the DC electrical power
transmitted from DC link 244 to a three-phase, sinusoidal AC
electrical power with pre-determined voltages, currents, and
frequencies. This conversion is monitored and controlled via
converter controller 262. The converted AC power is transmitted
from rotor-side power converter 220 to rotor filter 218 via rotor
filter bus 219 and is subsequently transmitted to generator rotor
122 via rotor bus 212, thereby facilitating sub-synchronous
operation.
[0032] Power conversion assembly 210 is configured to receive
control signals from turbine controller 202. The control signals
are based on sensed conditions and/or operating characteristics of
wind turbine 100 and electrical and control system 200. The control
signals are received by turbine controller 202 and used to control
operation of power conversion assembly 210. Feedback from one or
more sensors may be used by electrical and control system 200 to
control power conversion assembly 210 via converter controller 262
including, for example, conversion circuit breaker bus 230, stator
bus and rotor bus voltages or current feedbacks via second set of
voltage and electric current sensors 254, third set of voltage and
electric current sensors 256, and fourth set of voltage and
electric current sensors 264. Using this feedback information, and
for example, switching control signals, stator synchronizing switch
control signals and system circuit breaker control (trip) signals
may be generated in any known manner. For example, for a grid
voltage transient with predetermined characteristics, converter
controller 262 will at least temporarily substantially suspend the
IGBTs from conducting within line-side power converter 222. Such
suspension of operation of line-side power converter 222 will
substantially mitigate electric power being channeled through power
conversion assembly 210 to approximately zero.
[0033] FIG. 3 is a block diagram of an exemplary power system 300
suitable for use with electrical and control system 200 (shown in
FIG. 2) and wind turbine 100 (shown in FIG. 1). Power system 300 is
substantially similar to electrical and control system 200, and
similar components are numbered with similar reference numerals. In
the exemplary embodiment, power system 300 includes turbine
controller 202 communicatively coupled to a measurement device 302,
to power conversion assembly 210, and to a pitch system 304.
Alternatively, any suitable controller or control system may be
used instead of turbine controller 202. In the exemplary
embodiment, power conversion assembly 210 is also operatively
coupled to generator 118 that includes generator rotor 122 and
generator stator 120.
[0034] In the exemplary embodiment, turbine controller 202 controls
an operation of power system 300. Turbine controller 202 is
communicatively coupled to measurement device 302 by a measurement
bus 306. As used herein, the term "bus" includes a plurality of
conductors, but may also include a single conductor or an interface
by which two or more components may communicate wirelessly. Turbine
controller 202 receives one or more measurements from measurement
device 302 through measurement bus 306. Turbine controller 202 is
communicatively coupled to pitch system 304 by a pitch control bus
308 and/or by one or more slip rings (not shown). Turbine
controller 202 transmits one or more pitch commands through pitch
control bus 308 to pitch system 304 to adjust a pitch position of
one or more blades 108 of rotor 106. Moreover, turbine controller
202 is communicatively coupled to power conversion assembly 210 by
a converter bus 310. In the exemplary embodiment, converter bus 310
is a controller area network (CAN) bus. Alternatively, converter
bus 310 is a local area network (LAN) bus using an Ethernet bus
protocol, or any suitable bus. Turbine controller 202 transmits one
or more torque commands and/or one or more power commands to power
conversion assembly 210 through converter bus 310.
[0035] Measurement device 302 measures one or more characteristics
of electric power transmission and distribution grid 213. In the
exemplary embodiment, measurement device 302 includes one or more
current transformers electrically coupled to one or more
transmission lines 270 and/or to grid bus 242. Measurement device
302 measures an amplitude, a frequency, and/or a phase angle of a
voltage and/or a current of transmission line 270 and/or grid bus
242. In one embodiment, measurement device 302 includes first set
of voltage and electric current sensors 252 (shown in FIG. 2). In
the exemplary embodiment, measurement device 302 monitors the
frequency of each phase of the current of transmission line 270
and/or grid bus 242 (hereinafter referred to as the "grid
frequency") and detects if one or more phases of the grid frequency
are above a predefined limit (hereinafter referred to as an
"overfrequency condition"). During operation, the grid frequency
has a baseline of about 50 Hertz (Hz), about 60 Hz, or any suitable
frequency. In one embodiment, the predefined limit is between about
0% and about 10% above the baseline grid frequency. In another
embodiment, the predefined limit is between about 1% and about 5%
above the baseline grid frequency. In yet another embodiment, the
predefined limit is about 3% above the baseline grid frequency. In
the exemplary embodiment, the predefined limit is any suitable
limit set by turbine controller 202 or by any suitable controller.
Measurement device 302 transmits the measurements, including a
notification of a detected overfrequency condition, to turbine
controller 202. Alternatively, measurement device 302 transmits the
measurements to turbine controller 202, and turbine controller 202
detects if an overfrequency condition occurs.
[0036] In the exemplary embodiment, power conversion assembly 210
includes rotor-side power converter 220, line-side power converter
222, and converter controller 262 (all shown in FIG. 2). Power
conversion assembly 210 is a four quadrant power converter that can
provide a driving current and a braking current to generator 118 to
rotate and brake generator rotor 122 in a clockwise direction and a
counterclockwise direction. Alternatively, power conversion
assembly 210 includes any suitable configuration. In the exemplary
embodiment, power conversion assembly 210 transmits a rotor current
to generator rotor 122 through rotor bus 212. The rotor current
includes a rotor flux component that produces a magnetic flux
within generator 118 and a rotor torque component that produces a
torque within generator 118. In the exemplary embodiment, power
conversion assembly 210 controls a production of the rotor flux
component and the rotor torque component such that a phase angle of
the rotor flux component is substantially orthogonal to a phase
angle of the rotor torque component. Stator bus 208 is coupled
between power conversion assembly 210 and generator stator 120, and
stator bus 208 is also coupled to grid bus 242, as shown in more
detail in FIG. 2. Stator bus 208 carries a stator current that
includes a stator flux component that produces a magnetic flux
within generator stator 120 and a stator power component that
produces power to electric power transmission and distribution grid
213. In one embodiment, power conversion assembly 210 reduces or
minimizes a production of the stator flux component such that the
stator flux component is substantially zero, and a power factor of
generator stator 120 is substantially equal to one. Alternatively,
power conversion assembly 210 produces a suitable stator flux
component to create a desired magnetic flux within generator
118.
[0037] In the exemplary embodiment, pitch system 304 is at least
partially housed within rotor 106 and is operatively coupled to at
least one blade 108. Pitch system 304 rotates, or pitches, blades
108 to a desired position in response to one or more pitch commands
transmitted by turbine controller 202. Pitch system 304 facilitates
controlling a rotational speed of rotor 106 by adjusting an amount
of torque induced to blades 108 by wind 111. If an overfrequency
condition occurs, turbine controller 202 transmits one or more
pitch commands that direct pitch system 304 to pitch blades 108 to
a controlled position, such as a feathered position or any suitable
position, to prevent rotor 106 from exceeding a rated speed
(hereinafter referred to as an "overspeed condition").
[0038] In the exemplary embodiment, a flux gap 312 is defined
between generator rotor 122 and generator stator 120. The rotor
flux component flows through one or more windings (not shown) of
generator rotor 122 and creates a rotating magnetic field that
traverses flux gap 312. Torque produced by the rotor torque current
interacts with the rotating magnetic field and, when combined with
a rotation of a drive shaft 314, produces power within generator
stator 120. In the exemplary embodiment, drive shaft 314 includes
low-speed shaft 112 and/or high-speed shaft 116 (both shown in FIG.
2). The generated power is in the form of the stator power
component of the stator current within the windings of generator
stator 120, and the stator current is transmitted to electric power
transmission and distribution grid 213. In a similar manner, the
stator flux component may also flow through one or more windings
(not shown) of generator stator 120 to create a rotating magnetic
field across flux gap 312. The stator power component interacts
with the rotating magnetic field and, when combined with the
rotation of drive shaft 314, produces power within generator rotor
122. The generated power within generator rotor 122 is transmitted
to electric power transmission and distribution grid 213 through
power conversion assembly 210, stator bus 208, grid bus 242, and
grid coupling 272.
[0039] During operation, in the exemplary embodiment, when no
overfrequency condition is detected, power from electric power
transmission and distribution grid 213 energizes the windings of
generator stator 120 and/or the windings of generator rotor 122.
Wind 111 impacts blades 108 and induces a rotation of blades 108
and rotor 106, causing a rotation of drive shaft 314. Turbine
controller 202 calculates a desired power output of generator 118
and transmits one or more positive torque commands and/or one or
more positive power commands to power conversion assembly 210
through converter bus 310 to produce the desired power. As
described herein, the positive torque commands have a positive
torque amplitude that represents a torque to be created within
generator rotor 122. As described herein, the positive power
commands have a positive power amplitude that represents a power to
be generated within generator 118. Power conversion assembly 210
generates a suitable rotor current, including a rotor torque
current component and a rotor flux current component, based on the
torque commands and/or the power commands and transmits the rotor
current to generator rotor 122. The rotational speed of drive shaft
314 is multiplied by the torque created by the rotor torque current
component to generate power within generator 118. The power is
transmitted to electric power transmission and distribution grid
213 as described above.
[0040] During operation, if an overfrequency condition is detected
by measurement device 302 and/or turbine controller 202, turbine
controller 202 prepares to switch wind turbine 100, and more
specifically, generator 118 from a power generation mode to a power
consumption mode. As used herein, the term "power generation mode"
refers to a mode of operation in which generator 118 produces power
to be used in an electrical system. As used herein, the term "power
consumption mode" refers to a mode of operation in which generator
118 consumes power from the electrical system, rather than
producing power to the electrical system. Turbine controller 202
transmits one or more pitch commands to pitch system 304 to pitch
blades 108 to a controlled position. Pitch system 304 rotates
blades 108 to the controlled position to reduce or minimize an
amount of torque that wind 111 induces to blades 108. As such, a
rotational speed of blades 108 is reduced. In one embodiment,
blades 108 are pitched to a feathered position such that wind 111
induces substantially zero torque to blades 108, and the rotational
speed of blades 108 gradually reduces to substantially zero
revolutions per minute (rpm) due to frictional forces within rotor
106 and/or due to a braking effect of generator 118. Alternatively,
a rotation of blades 108 is not reduced to substantially 0 rpm, and
blades 108 continue to rotate while generator 118 is switched to
the power consumption mode.
[0041] Once blades 108 are pitched to the controlled position,
turbine controller 202 switches generator 118 from power generation
mode to power consumption mode. In alternative embodiments, any
suitable controller or control system, such as a wind farm
controller or a wind farm control system (neither shown), switches
generator 118 from power generation mode to power consumption mode.
In the exemplary embodiment, turbine controller 202 switches
generator 118 to power consumption mode by generating one or more
negative torque commands and/or negative power commands. As
described herein, a negative torque command has a negative torque
amplitude that represents a torque to be created within generator
rotor 122. As described herein, a negative power command has a
negative power amplitude that represents a power to be generated
within generator 118. Power conversion assembly 210 receives the
negative torque commands and/or the negative power commands and
outputs a resulting rotor current to generator rotor 122. In the
exemplary embodiment, a phase angle of the rotor current is
substantially inverted from a phase angle of the rotor current
generated during the power generation mode of generator 118. More
specifically, power conversion assembly 210 generates a rotor
current having an inverted phase angle of the rotor flux component
and an inverted phase angle of the rotor torque component with
respect to the rotor current transmitted to generator rotor 122
during the power generation mode.
[0042] Due to the reduced or minimized rotational speed of blades
108 and the inverted rotor current, generator 118 substantially
ceases producing power. Rather, generator 118 uses power from
electric power transmission and distribution grid 213 to produce
torque across flux gap 312. More specifically, the inverted phase
angle of the rotor current substantially reverses a direction of
current flow in generator 118. As such, current is drawn from
electric power transmission and distribution grid 213 during the
power consumption mode, rather than current being supplied to
electric power transmission and distribution grid 213 during the
power generation mode. Torque is generated in generator 118 due to
the interaction of the rotor torque current and the magnetic flux
within flux gap 312, in a substantially similar manner as described
above. However, during the power consumption mode, the torque
induces a rotation of drive shaft 314, rather than inducing a
generation of power as described above in the power generation
mode. The rotation of drive shaft 314 rotates rotor 106 and blades
108. It should be noted that blades 108 may rotate in the same
direction during the power consumption mode as when generator 118
operates in the power generation mode. As such, power from electric
power transmission and distribution grid 213 is consumed by
generator 118 and/or power conversion assembly 210 and the power is
used to drive the rotation of drive shaft 314.
[0043] If measurement device 302 and/or turbine controller 202
detects that the grid frequency is less than the predefined limit
(i.e., an overfrequency condition is not occurring), turbine
controller 202 switches generator 118 and/or wind turbine 100 from
power consumption mode to power generation mode using a
substantially similar, but reversed, procedure as described herein.
As such, wind turbine 100 and/or turbine controller 202 switches
generator 118 between power generation mode and power consumption
mode based on an existence of a detected overfrequency
condition.
[0044] FIG. 4 is a flowchart showing an exemplary method 400 for
controlling wind turbine 100 (shown in FIG. 1). In the exemplary
embodiment, measurement device 302 (shown in FIG. 3) detects 402 an
overfrequency condition within electric power transmission and
distribution grid 213, electrical and control system 200 (both
shown in FIG. 2), and/or power system 300 (shown in FIG. 3).
Turbine controller 202 pitches 404 one or more blades 108 (both
shown in FIG. 3) to a controlled position to prevent an overspeed
condition of rotor 106 (shown in FIG. 3) and/or blades 108, as
described above in reference to FIG. 3. After blades 108 are
pitched 404 to the controlled position, turbine controller 202
switches 406 generator 118 (shown in FIG. 3) to a power consumption
mode. In the exemplary embodiment, turbine controller 202 generates
one or more negative torque commands and/or one or more negative
power commands to switch 406 generator 118 to the power consumption
mode. Once generator 118 is operating in the power consumption
mode, generator 118 drives 408 rotor 106 using power supplied from
an electrical system, such as electric power transmission and
distribution grid 213, and/or any suitable electrical system. More
specifically, generator 118 uses power from electric power
transmission and distribution grid 213 to rotate drive shaft 314,
which rotates rotor 106 and blades 108. As such, in the power
consumption mode, generator 118 operates substantially as a motor
by using power from electric power transmission and distribution
grid 213 to rotate drive shaft 314, rotor 106, and blades 108.
[0045] A technical effect of the systems and method described
herein includes at least one of: (a) coupling a generator to a wind
turbine, and coupling the generator to an electrical system; (b)
detecting an overfrequency condition within an electrical system;
and (c) switching a generator from generating power to an
electrical system to consuming power from the electrical
system.
[0046] The above-described embodiments facilitate providing an
efficient and cost-effective power system for a wind turbine. The
power system detects overfrequency conditions within an electric
utility grid. If an overfrequency condition is detected, the power
system switches the wind turbine, or a generator within the wind
turbine, from a power generation mode to a power consumption mode.
The wind turbine consumes power during overfrequency conditions and
facilitates reducing or minimizing electric utility grid
overfrequencies. Moreover, the power system and wind turbine
described herein may facilitate reducing overfrequency conditions
more efficiently and more quickly than other known methods and
systems. As such, the wind turbine described herein may be coupled
to the electric utility grid while minimizing damage to the wind
turbine and/or to one or more electric utility grid components that
may result from otherwise uncorrected overfrequency conditions.
[0047] Exemplary embodiments of a wind turbine, power system, and
methods for controlling a wind turbine are described above in
detail. The methods, wind turbine, and power system are not limited
to the specific embodiments described herein, but rather,
components of the wind turbine, components of the power system,
and/or steps of the methods may be utilized independently and
separately from other components and/or steps described herein. For
example, the power system and methods may also be used in
combination with other wind turbine power systems and methods, and
are not limited to practice with only the power system as described
herein. Rather, the exemplary embodiment can be implemented and
utilized in connection with many other wind turbine or power system
applications.
[0048] Although specific features of various embodiments of the
invention may be shown in some drawings and not in others, this is
for convenience only. In accordance with the principles of the
invention, any feature of a drawing may be referenced and/or
claimed in combination with any feature of any other drawing.
[0049] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
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